1. Field of the Invention
This invention relates to catheters and catheter guidewire apparatus and methods for making same. More specifically, the present invention relates to a guidewire apparatus with improved torque and flexure characteristics.
2. State of the Art
Catheter guidewires have been used for many years to xe2x80x9cleadxe2x80x9d or xe2x80x9cguidexe2x80x9d catheters to target locations in animal and human anatomy. This is typically done via a body lumen, for example such as traversing Luminal spaces defined by the vasculature to the target location. The typical conventional guidewire is from about 135 centimeters to 195 centimeters in length, and is made from two primary componentsxe2x80x94a stainless steel core wire, and a platinum alloy coil spring. The core wire is tapered on the distal end to increase its flexibility. The coil spring is typically soldered to the core wire at a point where the inside diameter of the coil spring matches the outside diameter of the core wire. Platinum is selected for the coil spring because it provides radiopacity for better fluoroscopic or other radiologic imaging during navigation of the guidewire in the body, and it is biocompatible. The coil spring also provides softness for the tip of the guidewire to reduce the likelihood of unwanted puncture of a luminal wall or the damaging of this and/or other anatomy.
As mentioned, navigation of a guidewire through the anatomy is usually achieved with the assistance of radiographic imaging. This is conventionally done by introducing contrast media into the body lumen being traversed and viewing the guidewire in the body lumen using X-ray fluoroscopy or other comparable methods. A guiding catheter can be used, as well as a catheter configured to perform a procedure and to be directed to the target location by the guidewire. Catheters to perform coronary angioplasty and/or deploy stents are examples.
The guidewire is provided with a tip that is curved or otherwise bent to a desired angle so as to deviate laterally a relatively short distance. By rotation of the wire, the tip can be made to deviate in a selected direction from an axis of the guidewire about which it rotates. The catheter is advanced over the guidewire or the guidewire is inserted into a catheter so that the guidewire and the catheter cooperate to reach the target location. The guidewire can be advanced so that its distal end protrudes out the distal end of the catheter, and also pulled back in a proximal direction so as to be retracted into the catheter. The catheter enables introduction of contrast media at the location of the distal tip to enable the visualization of a Luminal space being traversed by the catheter and guidewire. The guidewire or catheter/guidewire combination are introduced into a luminal space such as a blood vessel and advanced therethrough until the guidewire tip reaches a desired luminal branch. The user then twists the proximal end of the guidewire so as to rotate and point the curved distal tip into the desired branch so that the device may be advanced further into the anatomy via the luminal branch. The catheter is advanced over the guidewire to follow, or track, the wire. This procedure is repeated as needed to guide the wire and overlying catheter to the desired target location. The catheter accordingly provides a means to introduce contrast media, and also provides additional support for the wire. Once the catheter has been advanced to the desired location, the guidewire may be withdrawn, depending upon the therapy to be performed. Oftentimes, such as in the case of balloon angioplasty, the guidewire is left in place during the procedure and can be used to exchange catheters.
As is known, a guidewire having a relatively low resistance to flexure yet relatively high torsional strength is most desirable. As the guidewire is advanced into the anatomy, internal frictional resistance resulting from the typically numerous turns and attendant surface contacts, decreases the ability to turn the guidewire and to advance the guidewire further within the luminal space. This, in turn, may lead to a more difficult and prolonged procedure, or, more seriously, failure to access the desired anatomy at the target location and thus a failed procedure. A guidewire with high flexibility helps overcome the problems created by this internal resistance. However, if the guidewire does not also have good torque characteristics (torsional stiffness), the user will not be able to twist the proximal end in order to rotate the distal tip of the guidewire to guide its advance as required.
Among the approaches suggested in the prior art for increasing the flexibility of the tip of a guidewire is that of cutting axially spaced grooves in and near the tip, with the depths of the grooves increasing toward the tip. See, for example, U.S. Pat. No. 5,437,288. Increasing the flexibility of a tubular member for use in catheter applications by making cuts therein is also known. The use of cuts to increase flexibility on one side only of a tubular guidewire is disclosed, for example, in U.S. Pat. No. 5,411,483. However, these prior art approaches do not inform the art how to increase the flexibility of the guidewire without also significantly diminishing its torsional stiffness. The result can be a guidewire with a machined portion that is very flexible, but which also has very low torsional strength.
It has been recognized that it would be desirable to have a guidewire that is very flexible at its distal tip, yet which retains a relatively high degree of torsional stiffness, facilitating its use and manipulation.
A catheter guidewire apparatus in accordance with principles of the invention comprises a thin elongate body of material having an longitudinal axis, and which is formed so as to define at a proximal portion a wire, and at a distal portion a configuration comprising a plurality of integrally formed beams disposed along the length of the thin elongate body. The integral beams extend axially and transversely of the body and are positioned and formed to give the guidewire flexibility while maintaining a relatively high degree of torsional stiffness. By manipulating the size, shape, spacing, and orientation of the beams, the torsional stiffness of the guidewire relative to its flexibility or beam stiffness can be selectively altered. These beams comprise the portions of the wall of a tubular body, or the outer portions adjacent the outer surface of a solid body member, which remain after cuts are machined into the body.
In more detail, in order to optimize the performance of the guidewire transverse and axial beams adjacent one to another are configured so that the strain (deformation) in the adjacent axial and transverse beams as defined above is as nearly as possible equal in magnitude when the guidewire is subjected to torsional and bending forces resulting from twisting and bending of the apparatus. The resistance to fatigue failure of the axial and transverse beams can also be matched, since a procedure can involve numerous repetitions of deformation of the beam elements as the guidewire is turned and advanced in tortuous anatomy, and the deformations can be large, this is also a good methodology to optimize performance. Combining the methods, and/or using the one that yields the best performance for a particular application results in improved performance over prior guidewires.
In a further more detailed aspect, the beams can be formed between cuts, by making cuts in pairs substantially opposite from one another and substantially parallel to each other. The spacing and depth of the cuts comprising the cut pairs being adapted to provide desired maximum flexibility while sacrificing minimal torsional strength.
In further detail, the elongate member with beams formed therein can be polished and corners rounded to minimize stress concentrations and increase resistance to fatigue.
Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.